subclassing EOGenericRecord to add a histroy feature

hello,

I'm attempting to subclass EOGenericRecord as to create a generic
"save history" function.

My current problem is creating the object to which i will save the history.

The basic code extending EOGenericRecord...

private void createHistoryObjects(){
            EOEditingContext eo = this.editingContext();
            EOEnterpriseObject newSet =
EOUtilities.createAndInsertInstance(eo, "abHistorySet");
            ((abHistorySet)newSet).setDateCreated(new NSTimestamp());
            eo.saveChanges();
}

is resulting in the following error -

 java.lang.IllegalStateException: Unable to find entity for object
{values = {status = ; values = (); entityName = ; rowid = ;
dateCreated = 2006-01-26 03:28:17 Etc/GMT; entityID = ; }; this = ">";
}
             Reason:             Unable to find entity for object
{values = {status = <com.webobjects.foundation.NSKeyValueCoding$Null>;
values = (); entityName =
<com.webobjects.foundation.NSKeyValueCoding$Null>; rowid =
<com.webobjects.foundation.NSKeyValueCoding$Null>; dateCreated =
2006-01-26 03:28:17 Etc/GMT; entityID =
<com.webobjects.foundation.NSKeyValueCoding$Null>; }; this =
"<abHistorySet 4fe1f9 <EOTemporaryGlobalID: 0 0 -64 -88 0 40 0 0 -8 25
1 0 0 0 1 9 4 -63 24 -18 84 -109 127 34>>"; }

I'm really not sure what direction to go in. What rule am I breaking?

Many thanks,
Matt